Log cabin type structures are typically small rectangular rooms formed of horizontally laid relatively thick planks or so called "logs" which may be 11/4to 3 inches thick. The use of the relatively thick wood provides a high degree of thermal insulation, and also provides an attractive appearance both inside and out without the requirement for additional wall finishings.
This type of structure is typically used for domestic saunas. This type of construction may also be used however for outdoor structures such as vacation cottages and chalets, and garden structures such as swimming pool changing huts and the like.
It is prime feature of this type of construction, that it can be readily erected by a householder with only common hand tools. In addition, at least when a sauna is constructed in a home for example the structure must be erected in a relatively confined space.
"Log" structures such as these are found to exhibit some expansion and contraction or warping of individual planks or "logs" and it is essential that the corners of the structure be held together by a strong and yet simple fastening system. If this is not done, then the logs will tend to loosen, or become unsealed. This is particularly undesirable in the case of a sauna where the interior of the structure is subjected to high temperatures, and to a high humidity. If the vapor escapes into the home, it may cause mildew and rot in other parts of the home and is highly unsatisfactory.
Similarly, when such structures are used for any outdoor construction, it is obviously desirable that the logs should remain held tightly together so that they will provide a good hermetically sealed wall.
In the past, various proposals have been made to overcome this problem. For example, one popular system employs logs which are notched at their corners, and overlap one above the other. A series of wooden pegs pass through grooves formed in the corner portions of the logs. Such a system is extremely complex, and in particular, the grooves must be machined with a high degree of accuracy so that they will line up once the logs are arranged, since otherwise the wooden pegs cannot be inserted. In practice, it is almost impossible to obtain the necessary high degree of manufacturing tolerance, when machining the logs. In addition, even though the logs are securely pegged together, they can still move somewhat upwardly and downwardly causing them to be gradually loosened.
Another system has been proposed in which some form of exterior fastening is arranged around the outside of the corners of the structure.
At first sight it would appear that the simplest way of solving the problem is simply to run a lengthwise metal rod up through overlapping corners of the logs with fastenings at the top and bottom of the rod. This will apply vertical pressure to the overlapping notched corners of the logs and hold them together. However, such a system does nothing to prevent slight endwise movement of the logs. It does not therefore provide a satisfactory solution.
In addition to all of these problems, it is essential that a good vapor tight seal should be provided at the corners of the logs. The logs are provided with conventional lengthwise interlocking tongues and grooves which provide as far as possible a good vapour tight seal provided they are securely fastened. However, at the corners, the sealing of the overlapping interlocking portions of the logs presents a more difficult problem. Unless accurately machined mating surfaces are provided in the corners, and unless such surfaces are held together by constant pressure, the logs will tend, as a result of expansion and contraction, to work loose thereby opening up the corners.